This invention relates to digital print heads and in particular to ink jet print head cartridges and to housing and the provision ofexternal electrical connections therefor.
Ink jet print head cartridges or modules are known in which a casing houses a plurality of ink jet nozzles from which droplets of ink may be ejected selectively as required by ink ejection means and electronic circuits for controlling operation of the ink ejection means. One known form of ink jet print head includes, for each ink ejection nozzle, an ink chamber communicating with the ink ejection nozzle and a resistive element for heating the ink in the ink chamber so as to eject a droplet of ink from the nozzle. A pulse of electrical current is passed through the resistive element to cause the required heating of the ink in the associated ink chamber. Electronic driver circuits of the print head control generation of the pulse of electrical current. The driver circuits are controlled by print control signals generated externally of the print head module by electronic control circuits operating to cause ejection of ink droplets selectively in a sequence of printing cycles from selected ones of the nozzles such as to produce a required imprint on a print receiving medium.
The ink jet print head module includes a reservoir of ink and, as ink is ejected in droplets from the nozzles during operation of the print head, the ink in the reservoir is gradually depleted. In known commercially available ink jet print head modules, when the ink in the reservoir has been depleted to a low level the entire module is replaced by a new module containing a reservoir full of ink. Accordingly the module is constructed to be readily removable and replaceable by a user of printing apparatus incorporating such ink jet print modules. The module is provided with a set of electrical contacts which, when the module is removably mounted in the printing apparatus, engage with a corresponding set of electrical contacts of the printing apparatus to connect the external control circuits to the driver circuits of the print head module.
In one commercially available ink jet print module, the nozzles of the print head are located in a first planar face of the module and the set of electrical contacts is located on an adjacent face extending substantially perpendicular to the first face. While this construction and relative location of the nozzles and of the set of electrical contacts is satisfactory in many constructions of printing apparatus, it does impose restrictions on the construction of the printing apparatus with regard to the insertion into and removal from the printing apparatus of the print head modules.
Generally the commercially available print head modules are used in non-secure printers for example output printers connected to and operated by personal computers. However it is also proposed to use commercially available ink jet print head modules in postage meters for printing postal indicia on mail pieces. It will be appreciated that because postage meters are used to dispense postage value it is required that the print head is operated in a secure manner and postal authorities may require use of an ink that is different from inks used in print head modules used generally for other purposes. Accordingly it is desired to ensure that only authorised print head modules are utilised in the postage meter.
According to the invention an ink jet printhead includes an ink jet print module and a cartridge housing; said ink jet print module including a plurality of ink jet nozzles in a first exterior surface of said module; selectively operable driver means to eject ink from selected ones of said nozzles and a set of electrical contacts connected to said driver means and located on a second exterior surface of the module; said ink jet print module being housed in said cartridge housing; said cartridge housing including a wall and an aperture in said wall through which said first surface extends so that said ink jet nozzles are located exterior to the housing; an element extending from said housing and supporting a set of electrical terminals; and electrical connection means providing electrical interconnections between electrical contacts of said set of electrical contacts and electrical terminals of said set of electrical terminals.
Preferably the electrical terminals are located on a printed circuit board, said printed circuit board extending from the element into the interior of the housing; said printed circuit board being provided with a set of electrical contact pads corresponding to said electrical contacts of the print head module, the electrical contact pads respectively being in electrical contact engagement with corresponding ones of the electrical contacts and the printed circuit board includes electrical tracks extend interconnecting the electrical terminals and the electrical contact pads.
If desired the terminals may be connected respectively to correspondingly located electrical contacts of the print head module or at least some of the terminals may be connected to electrical contacts of the print head module that are not located corresponding to the terminals.
The housing may have a planar side wall and the element supporting the terminals may extend substantially perpendicular to the planar side wall.